The field of this invention is analyte determination, particularly electrochemical analyte determination and more particularly the electrochemical determination of blood analytes.
Analyte detection in physiological fluids, e.g. blood or blood derived products, is of ever increasing importance to today""s society. Analyte detection assays find use in a variety of applications, including clinical laboratory testing, home testing, etc., where the results of such testing play a prominent role in diagnosis and management in a variety of disease conditions. Analytes of interest include glucose for diabetes management, cholesterol, and the like. In response to this growing importance of analyte detection, a variety of analyte detection protocols and devices for both clinical and home use have been developed.
One type of method that is employed for analyte detection is an electrochemical method. In such methods, an aqueous liquid sample is placed into a reaction zone in an electrochemical cell comprising two electrodes, i.e. a reference and working electrode, where the electrodes have an impedance which renders them suitable for amperometric measurement. The component to be analyzed is allowed to react directly with an electrode, or directly or indirectly with a redox reagent to form an oxidisable (or reducible) substance in an amount corresponding to the concentration of the component to be analyzed, i.e. analyte. The quantity of the oxidisable (or reducible) substance present is then estimated electrochemically and related to the amount of analyte present in the initial sample.
Where the physiological sample being assayed is whole blood or a derivative thereof, the hematocrit of the sample can be a source of analytical error in the ultimate analyte concentration measurement. For example, in electrochemical measurement protocols where the analyte concentration is derived from observed time-current transients, hematocrit can slow the. equilibration chemistry in the electrochemical cell and/or slow the enzyme kinetics by increasing the sample viscosity in the cell, thereby attenuating the time current response and causing analytical error.
As such, there is great interest in the development of methods of at least minimizing the hematocrit originated analytical error. In certain protocols, blood filtering membranes are employed to remove red blood cells and thereby minimize the hematocrit effect. These particular protocols are unsatisfactory in that increased sample volumes and testing times are required. Other protocols focus on the determination of the capillary fill time. However, these protocols add complexity to both the strips and devices that are used to read them. In yet other embodiments, hematocrit is separately determined using two additional electrodes, which also results in more complex and expensive strips/devices.
As such, there is continued interest in the identification of new methods for electrochemically measuring the concentration of an analyte in a physiological sample, where the method minimizes the analytical error which originates with the hematocrit, of the sample.
Relevant Literature
Patent documents of interest include: 5,942,102 and WO 97/18465.
Methods and devices for determining the concentration of an analyte in a physiological sample are provided. In the subject methods, the physiological sample is introduced into an electrochemical cell having a working and reference electrode. A first electric potential is applied to the cell and the resultant cell current over a first period of time is measured to determine a first time-current transient. A second electric potential of opposite polarity is then applied to the cell and a second time-current transient is determined. The preliminary concentration of the analyte (C0)is then calculated from the first and/or second time-current transients. This preliminary analyte concentration, less a background value, is then multiplied by a hematocrit correction factor to obtain the analyte concentration in the sample, where the hematocrit correction factor is a function of the preliminary analyte concentration and the ratio of 2 current values (xcex3) within the time-current transient of the electrochemical cell. The subject methods and devices are suited for use in the determination of a wide variety of analytes in a wide variety of samples, and are particularly suited for the determination of analytes in whole blood or derivatives thereof, where an analyte of particular interest is glucose.